<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    button {
        position: fixed;
        left: 20px;
        top: 200px;
    }
    iframe {
        position: absolute;  /* 或 fixed */
        z-index: 1000;      /* 确保这个值比其他元素大 */
        width: 100%;
        height: 100%;
        border: none;
        opacity: 0.5;
    }
</style>
<body>
    <h1>这是B页面</h1>
    <iframe src="http://localhost:3000/a.html"></iframe>
    <button>钓鱼按钮</button>
    <script></script>
</body>
</html>
